TPMS sensors: Modern vehicles have tire-pressure sensors in or near each wheel. Many transmit a unique sensor ID by short-range radio. Bartec describes diagnostic equipment being capable of displaying both the vehicle's VIN and TPMS sensor IDs.
Application from Tortured Genius Enterprises LLC, describes a system intended to:
intercept TPMS radio transmissions from passing vehicles;
extract the sensors' unique identifiers;
associate those identifiers with a particular vehicle;
determine vehicle location;
connect the identifier with outside databases;
potentially retrieve make, model, VIN and owner information;
maintain historical observations;
predict future locations/behavior;
direct law enforcement to intercept a vehicle.
https://networks.imdea.org/your-cars-tire-sensors-could-be-u...